1. Field of the Invention
The present invention relates to a thermoplastic film label composite that has a printable, untreated, cavitated surface and a method of making such label composites. In particular, the untreated, cavitated surface provides a stable print medium that exhibits excellent printability properties, without sacrificing initial adhesion or fiber tear.
2. Description of Related Art
In the packaging industry, it is desirable to place a label on a packaging material to either advertise and promote the product therein, or to simply identify the ingredients thereof. Throughout the years, a number of label stock materials have been used, ranging from paper to polymeric label stock materials.
Polymeric label stock materials have been found to be particularly attractive because they provide certain characteristics missing in paper labels. These characteristics include: durability, strength, water resistance, curl resistance, abrasion resistance, gloss, transparency, etc.
Polymeric label stock materials must meet a number of commercial and manufacturing requirements. They must be economical and suitable for manufacturing processes, such as cast film extrusion or blown film extrusion. For example, a formed film material must be capable of hot-stretching without deleterious effect. In this regard, it is generally advantageous to hot-stretch and anneal a formed film, so as to biaxially orient the film and impart a stiffness to it that is different in the machine and transverse directions.
Preferred polymeric label stock materials generally have a printable face or front-side (the face or front-side being the side of the label opposite to and not in direct contact with the substrate), and are die-cuttable, as well as matrix-strippable when used in a pressure-sensitive label construction. Upon die-cutting, the labels can be applied to a substrate via, e.g., a pressure-sensitive label. Cold glue adhesives are viewed as an economical alternative to pressure-sensitive labels that can be suitable for cut-and-stack applications. A label adhered to a substrate with a cold glue adhesive provides good initial adhesion, while minimizing visual defects.
Olefins, including olefin blends, are examples of polymeric materials that may be employed to meet the demands of polymeric, die-cut label manufacture. The relatively low cost of olefinic resins, coupled with their high strength that allows for low-caliper film, tends to minimize overall material cost. For example, hot-stretched polypropylene and/or polyethylene provides sufficient stiffness in the machine direction, even at a relatively low-caliper thickness, for adequate print registration and dispensing. Further, hot-stretched polypropylene and/or polyethylene provides sufficiently low tensile modulus and, in particular, sufficiently high elongation in the transverse direction for conformability.
Oriented cavitated film compositions are generally known in the art. For example, U.S. Pat. No. 4,632,869 discloses an opaque, biaxially oriented film structure having a polymer matrix with a strata of voids, the voids containing spherical void-initiating particles of polybutylene terephthalate. The structure may also include thermoplastic skin layers, and the film can include from about 1% to 3% by weight of a pigment such as TiO2 or colored oxides.
U.S. Pat. No. 4,741,950 discloses a differential opaque polymer film with a core layer containing numerous microscopic voids, a rough-appearing wettable first skin layer which contains an antiblocking agent such as silica, silicate, clay, diatomaceous earth, talc and glass, and a second wettable skin layer with a smooth appearance which may be metallized. TiO2 may be present in the core and/or first skin layer. The film allows a light transmission of 24%.
U.S. Pat. No. 5,176,954 discloses a non-symmetrically layered, highly opaque, biaxially oriented polymer film with a core containing numerous microscopic voids and at least about 1% by weight of opacifying compounds; a first skin layer on one surface of the core containing up to about 12% by weight of inorganic particulate material; and a second skin layer on the other surface of the core. The ""954 patent also discloses the benefit which accrues from the addition of inorganic particles such as titanium dioxide to whiten the surface of the outer skin layer of the film structure. The increase in whiteness yields an excellent surface for printed graphics. A further benefit resulting from increased whiteness in the outer skin layer of the film is that it permits the printing of laminated or unlaminated film structures without the need for white ink, offering a significant savings to the end user.
In addition, a number of films with ink-retention properties have been developed. For example, U.S. Pat. No. 6,331,343 describes an oriented film that has at least one fibrous surface. The film includes a melt-processed, immiscible mixture of a semicrystalline polymer component and a void-initiating component. The fibrous surface provides the film with a surface area that renders the film useful in applications such as ink-receptive substrates, wipes, paper-like films and as backings for tape. The ""343 patent is hereby incorporated by reference in its entirety.
U.S. Pat. No. 6,194,506 discloses a polyolefinic resin film that has a calcium carbonate dispersed therein to act as nuclei forming microvoids in the polyolefin film. Thus, the film is rendered with a specific oil absorption. The ""506 patent is hereby incorporated by reference in its entirety.
U.S. Pat. No. 6,086,987 discloses a synthetic paper made of a stretched resin film obtained by stretching a resin film having as a support a resin composition containing (a) from 30-80% by weight of crystalline polyolefin resin and (b) from 70-20% by weight of milled calcium carbonate particles at a temperature lower than the melting point of the crystalline polyolefin. The ""987 patent is hereby incorporated by reference in its entirety.
U.S. Pat. No. 6,074,747 discloses an ink-printable release coating composition including a substrate having a pressure-sensitive adhesive on a back surface and an ink-printable cured release coating on the face surface. The release coating includes a polymer selected from the group consisting of silicones, fluoroacrylates and polyurethane polymers; and resin particles that are different from the polymer to release any abutting materials without ruining the print thereon. The ""747 patent is hereby incorporated by reference in its entirety.
U.S. Pat. No. 5,667,872 discloses a synthetic paper with a multilayer structure including a biaxially stretched film of an olefinic polymer having a melting point of 130xc2x0 C. to 210xc2x0 C. containing 5 to 40% by weight of inorganic fine powder as a base material. Adhered to at least one surface of the base material is a uniaxially stretched layer of a propylene-xcex1-olefin copolymer having a melting point at least 5xc2x0 C. lower than the melting point of the base material and from 8 to 65% by weight of inorganic compound. The ""872 patent is hereby incorporated by reference in its entirety.
Co-pending U.S. Ser. Nos. 09/770,960 and 10/098,806 disclose labels for use with cold glue. They fail to disclose an untreated, cavitated skin layer that serves the dual role of a printing and laminating surface.
There are disadvantages, however, associated with prior art thermoplastic film label composites. They can be far too complex, including, for example, the formation of fibrous surfaces and/or the need for secondary operations. Examples of needed secondary operations include operations designed to attain a suitable ink-retention property, such as annealing or surface treatments, such as ozone, corona discharge, and plasma.
A further disadvantage associated with prior art thermoplastic film label composites is that they are not designed to be printed on their reverse side, i.e., their back-side, where the advertisement or promotion may be observed through the packaging material, e.g., through a transparent bottle of polyethylene terepthalate (PET) or glass, or where the advertisement or promotion, e.g., coupon or game piece, may be observed upon removing the film label composite from an opaque packaging material.
An object of the present invention is to provide a novel thermoplastic film label composite with a printable, untreated cavitated surface that meets the requirements of the packaging industry and overcomes the disadvantages of the prior art. In particular, the untreated, cavitated surface provides a stable print medium that exhibits excellent printability properties, without sacrificing initial adhesion or fiber tear when laminated to a substrate.
A further object of the invention is to provide a novel thermoplastic film label composite that has a printed image on both the front-side and back-side of the label. Thus, in addition to the typical image on the front-side of the label that, e.g., promotes the product therein, there may be provided, e.g., an advertising logo, promotion, coupon, game piece or ingredient list on the back-side of the label that can be viewed through the packaging material, e.g., through a transparent bottle. Alternatively, a coupon or game piece may be printed on the back-side of the label so that it can be viewed when the label is removed from, e.g., an opaque container, in, e.g., a hot-melt adhesive application.
A still further object of the invention is to provide a method of manufacturing the novel thermoplastic film label composite.
There is provided a thermoplastic film label composite, including at least:
(a) a base layer comprising a thermoplastic polymer, wherein the base layer has a first side and a second side; and
(b) a first skin layer comprising a thermoplastic polymer and a cavitating agent, wherein the first skin layer has a first side and a second side, and the first skin layer is untreated.
The base layer may also comprise a cavitating agent. In addition, the thermoplastic film label composite may be laminated at the first skin layer to a substrate by employing an adhesive therebetween. Prior to laminating the thermoplastic film label composite at the first skin layer to a substrate, the first skin layer may have an image printed thereon.
There is also provided a method of manufacturing the thermoplastic film label composite, including at least the steps of:
(i) coextruding melts corresponding to the individual layers of the film label composite to form a coextruded sheet;
(ii) casting the coextruded sheet;
(iii) quenching the coextruded sheet; and
(iv) orienting the coextruded sheet to form a film.
The thermoplastic film label composite may be manufactured (i) with a second skin layer on a side of the base layer opposite the first skin layer, (ii) with one or more tie layers between the base layer and the first skin layer, and/or (iii) with one or more tie layers between the base layer and the second skin layer (if any). The second skin layer may be surface-treated, metallized, and/or coated. The second skin layer may also have an image printed thereon.